In recent years there has been increasing interest in the use of ice blasting techniques to treat surfaces. For certain applications, ice blasting provides significant advantages over chemical surface treatment, blasting with sand or other abrasive materials, hydro-blasting, and blasting with steam or dry ice. The technique can be used to remove loose material, blips and burrs from production metal components, such as transmission channel plates after machining, and even softer material, such as organic polymeric materials, including plastic and rubber components. Because water in either frozen or liquid form is environmentally safe, and inexpensive, ice blasting does not pose a waste disposal problem. The technique can also be used for cleaning surfaces, removing paint or stripping contaminants from a surface, without the use of chemicals, abrasive materials, high temperatures, or steam.
Because of these apparent advantages, ice blasting has generated significant commercial interest which lead to the development of a variety of technologies designed to deliver a high pressure spray containing ice particulates for performing particular surface treatment procedures. Some of these technologies are shown, for example, in U.S. Pat. Nos. 2,699,403; 4,389,820; 4,617,064; 4,703,590; 4,744,181; 4,965,968; 5,203,794; and 5,367,838. Despite all the effort devoted to ice-blasting equipment, the currently available equipment still suffers significant shortcomings that lead to job interruption and downtime for equipment maintenance. This is a particular disadvantage in using ice blasting in a continuous automated production line to treat surfaces of machined parts.
In general, in the prior art equipment, the ice particulates are mechanically sized, a process that can cause partial thawing of ice particulates so that they adhere together, producing larger particulates. As a result, there is not only a wide distribution in the size of ice particulates produced, and the velocity at which these particulates are ejected from a nozzle onto the surface to be treated, but also frequent blockages that necessitate equipment downtime for clearing the blocked area. Moreover, in the available equipment, the ice particulates are retained in storage hoppers, where they are physically at rest, while in contact with each other. This results in ice particulates cohering to form larger ice blocks that ultimately cause blockages with resultant stoppage of the ice blasting operation due to an insufficient supply of ice particulates to the blasting nozzle. In other equipment, the ice particulates flow along a path with abruptly varying cross-sectional area for flow. This frequently causes the accumulation of fine ice particulates in certain low pressure areas. This accumulation also ultimately results in blockage of the apparatus, causing the ice blasting operation to come to an unscheduled stop.
There yet exists a need for ice-blasting apparatus, and a method of ice blasting, that can be carried out continuously, with minimal risk of unscheduled stoppages due to ice blockages forming in the apparatus. Such an apparatus, and method of its operation, will allow more efficient ice-blasting operations, reducing labor costs for unscheduled stoppages, labor costs incurred in freeing the equipment of blockages, and permit more ready integration of ice blasting into an automated production line.